D=b²-4ac
<span>------------------
5х²-4х-1=0
D</span>=(-4)²-4*5*(-1)=16+20=36=6²
<span>----------------------
3х-х²+10=0
D=</span>(3)²-4*(-1)*10= 49 = 7²
---------------------------------
<span>х²-6х+9=0
D</span>=(-6)²-4*1*9=36-36=0
----------------
2х+3+2х²=0<span>
D=</span>2²-4*2*3=4-24=-20